An increasing desire to transition from traditional fossil fuels for energy production coupled with an aging nuclear power infrastructure presents a critical demand for new power production designs. Advanced Generation IV reactor designs offer potential solutions to this looming future demand. Of these Gen IV reactors, pool-type sodium fast reactors are a leading candidate with hundreds of reactor years of operation and many inherent benefits over traditional light water reactors. However, prior to licensing a commercial sodium fast reactor, a mechanistic source term assessment is likely required. An assessment of the current state of knowledge for sodium fast reactor source term assessment was conducted at Argonne National Laboratory. From this, several key gaps were identified within the knowledge base. Fission product scrubbing via bubble release was of particular importance due to its impact on the overall source term calculation and associated uncertainty. Gaseous fission products entering the coolant pool following fuel pin failure have the potential to be transported directly to cover gas region. Solid/liquid fission products may either be injected into the coolant pool fluid or be entrained within gaseous fission products. While the coolant pool itself is expected to scrub the majority of radionuclides, those becoming entrained within bubbles have the potential to be transported directly to the cover gas region. From the cover gas, there is a considerably greater risk of release to the environment. To better understand this phenomenon, recent efforts in sodium fast reactors have been towards developing computational tools to model fission product retention following accident scenarios. Researchers at Argonne National Laboratory have developed the Simplified Radionuclide Transport code to model fission product transport. The model is able to estimate fission product types and quantities based on failure criteria and then predict their transport from the fuel pin to the coolant pool, and eventually to the environment. The bubble scrubbing portion of this code utilizes classical aerosol scrubbing theories to predict an overall decontamination factor. To validate this code, experimental data is needed. Currently, there are limited bubble scrubbing data in a sodium coolant pool. This thesis aims to validate the Simplified Radionuclide Transport bubble scrubbing code in a sodium environment while conducting a parametric study to analyze the effects of aerosol size, bubble size, pool temperature, pool depth, aerosol density, and aerosol concentration. Through a series of experiments, it was determined that aerosol sizes ranging from 0.001 to 1 microns are of primary concern as aerosols in this range have a ratio of aerosol mass entering the sodium pool from the fuel pin to aerosol mass exiting the sodium pool to the cover gas region of less than 10. The experimental results were found to match the trends found in the scrubbing model closely, but significantly more scrubbing was seen experimentally. Decreasing bubble size and increasing pool depth and aerosol density were all found to increase scrubbing both experimentally and theoretically. Pool temperature was found to have a negligible effect on scrubbing amounts; however, this was largely due to a subsequent increase in bubble size corresponding to increasing temperatures. Varying aerosol concentration was found to have no effect on scrubbing ratios. A final series of tests was conducted for a more prototypic fuel pin failure with a heterogenous bubble swarm. From these tests, it was found that the experimental scrubbing quantities were larger than for the single bubble case. Overall, it was found that the simplified bubble transport scrubbing code accurately models the trends of the bubble scrubbing but provides a conservative estimate of scrubbing quantities.

In the evaluation of reactor sites, the dose rate from iodine is the controlling factor in the distance criteria. Several experiments which were conducted on the retention of fission products by sodium are described, and some of the results are given. These experiments included fission product solubility in sodium, release of iodine bubbles from a sodium pool, and in-pile transient melting of fuel disks in sodium. The retention results of the last experiment were compared with these for an organic coolant. It is concluded that sodium retains all of the iodine. (D.L.C.).

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